Cool Science Experiments to Try at Home

Cool Science Experiments to Try at Home: Chemistry

Cabbage Juice pH Chemistry Lab

Acids and bases are extremely important in chemical reactions. In this experiment we will use cabbage juice to help us identify many common household chemicals as acids or bases by changes in its color. It looks cool too!

What you'll need: •

Red cabbage leaves

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Large bowl or glass pitcher

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everal small clear glass or plastic cups paper "ixie cups are okay if you can#t get clear cups$

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trainer% trainer% colander or funnel with cheesecloth or coffee filter paper

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cissors

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&offee filter papers the white ones are best$

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'oiling water

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(ousehold ammonia

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'aking soda sodium bicarbonate$ dissolved in a little water

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)ashing )ashing soda sodium carbonate$ dissolved in a little water

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"ish soap

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Laundry detergent dissolved in a little water if you#re using powder$

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hampoo clear is best$

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Antacid tablets or powder dissolved in a little water

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Lemon juice

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*range juice

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+inegar

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elt,er water or soda

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&ream of tartar dissolved in a little water

Also be sure to ask your mom% dad or another adult to help- you can impress them with the magical color changes!

Basic Experimental Procedure: . /ear /ear or cut cabbage leaves leaves into fairly small pieces and and place them in a large bowl or glass pitcher. 0. 1our boiling boiling water over over the leaves leaves to cover cover them completely% completely% then let this 2tea2 steep for several minutes until the li3uid turns a purplish color. color. 4. *nce it has cooled% remove remove most of the leaves or filter them using using a strainer strainer%% colander or funnel with coffee filter. It#s the juice that we want. 5ou could also simply spoon out the juice without removing the leaves if you like. 6. 1our a little cabbage juice into each each of your small small plastic or glass cups. /he /he amount you use will depend on the si,e of your cup% but don#t use too much at first% maybe -0 tablespoons 7-48 milliliters or ml$ 7. Add a small small amount amount a few drops drops at first$ first$ of one one of your test test solutions solutions to the the cup of cabbage juice and note the change in color. 'e sure to set aside one cup of cabbage  juice that you will not add add anything to so you you can compare compare the color changes. changes. /his cup is called the 2control.2 9. Add small small amounts amounts of other test test solutions solutions to other cabbage cabbage juice juice cups and and note the color you get. "on#t add more than one test solution to any cup- we want to see what color each makes before we do any mixing. If you started with most of the test solutions listed you should have a range of colors: red% pink% purple% violet% blue% green and possibly even yellowish green. ;. /ry /ry a few other common household li3uids% including plain water water.. )hat colors do they produce when added to cabbage juice<  Adanced Experimental Experimental Procedure: Procedure: . Identify Identify a test solution solution that that turned the the cabbage cabbage juice green green or blue probably probably soap soap or ammonia% don#t use baking soda yet$. )e#ll call this a 2base2. 0. =ext identify identify a test solution solution that that turned the the cabbage cabbage juice red or pink pink probably probably lemon juice or vinegar$. )e#ll call this an 2acid2. 4. =ow using using a fresh cabbage cabbage juice juice cup% slowly slowly add some some of your 2base2 2base2 solutionsolution- just just as you did before- until it again turns the cabbage juice blue or green. 6. /hen very very slowly slowly add some of your your 2acid2 2acid2 solution solution to the same cup cup until the cabbage cabbage  juice mixture begins to return return to its original purple color. color. /his /his is called a neutrali,ation or titration experiment. 7. lowly lowly continue continue to add more more of your your 2acid2 2acid2 solution solution to the cup cup until the color color changes from purple to red or pink. 5ou#ve 5ou#ve demonstrated that the color changes in this experiment are reversible.

9. /ry /ry repeating the experiment backwards% backwards% i.e. start start with the 2acid2 to make make a pink or red solution% then slowly add 2base2 to change the color back to purple% then green or blue. /ry different combinations of acids and bases. ;. >or one one last experiment% use your cup cup with baking baking or washing soda added added to the cabbage juice it should be bluish colored$. lowly add a few drops of one of your 2acid2 test solutions like vinegar or lemon juice$. )hat happens this time<

What's Happening: Red cabbage contains a compound called anthocyanin% which is a type of molecules called flavonoids. /hese compounds are often used as pigments or stains because they are very colorful% but what makes anthocyanin even more interesting is that the color it produces varies dramatically dramatically depending on the p( of the solution. p( is a way that chemists characteri,e characteri,e acids and bases. /his has to do with the concentration of hydrogen ions in the solution acids have higher concentrations of hydrogen ions% bases lower$% but for our purposes we can just consider acids and bases as opposites% and think of p( as a scale or ruler% ruler% with acids at the low end numbers between 8-9$ and bases at the high end number typically between ?-6$. A p( of ; means the solution is neutral neither acid nor base% or both% depending on your point of view. 1ure water is neutral% with a p(@;. /he lower the p(% the stronger the acid and the higher the p( the stronger the base. p( numbers close to ; are weak acids or bases respectively. 1igments like anthocyanin that change color with p( are called indicators. Identifying the strength of acids and bases is one of the most important tests used in chemistry% chemistry% as p( is one of many factors that determines how different molecules or chemicals will react when combined. 5ou can learn much more about p( chemistry% acids% acids% bases and indicators in the references at the end of this experiment.B

Acidic solutions acids$ like vinegar% lemon and other citrus juices which contain citric acid$ and sodas carbonic acid% or carbon dioxide dissolved in water$ make the anthocyanin in cabbage juice turn reddish colors% while basic solutions bases$ like ammonia% baking soda and soaps turn cabbage juice bluish or greenish colors even yellowish if the base is really strong$. 5ou can actually measure the p( by making a color chart like the one below% with red at the low end% followed by pink% purple or violet% blue% blue-green or a3ua% green and

finally yellowish green at the high end. trong acids like lemon juice turn cabbage juice red% strong bases like ammonia turn it green% and other solutions generally fall somewhere in between. Acids add more hydrogen ions to a solution% while bases remove hydrogen ions from a solution% so we can adjust the p( to any value we want by carefully combining acids and bases together. >or example% if we have a vinegar solution that is strongly acidic% we can raise the p( by slowing adding a base like ammonia which will remove some of the extra hydrogen ions from the solution. If we add just a little we might change the p( from 0 to 7% making a weaker acid% but by adding a little more base we remove enough hydrogen ions to raise the p( to ; or neutrali,e the solution. >inally% >inally% by adding even more base we can remove more and more hydrogen ions% raising the p( until the solution becomes a strong base. /his process is completely reversible% so we could add more acid i.e. more hydrogen ions$ and lower the p( just as easily. *f course when we mix chemicals like this other reactions may take place as well% so it#s always very important to follow the instructions in an experiment like this unless you are very familiar with the chemicals you are using. /hat#s what happens when you mixed vinegar with baking soda. /hese two chemicals reacted to produce carbon dioxide gas all the bubbles you saw$. >ortunately the chemicals used in this experiment are relatively safe.

!ariations and "elated Actiities: Anthocyanin Anthocyanin is also found in many other foods: Red Cinger herbal teaD Erape juice or grapesD Red onionsD 1lumsD FggplantD &herriesD RadishesD and 'lackberries. /ry making your idicator solution from any of these. "o they work any better< Another way to test for acids or bases is to use a piece of paper that has been treated with a special p( indicator. )e can use our cabbage juice for this. imply take one or two coffee filter papers the white kind works best$ and place them in your bowl of cabbage juice for several minutes you can fold them if necessary$. /he juice will stain the paper purple% which means some of the anthocyanin anthocyanin will bond or stick to the paper. After it becomes well stained% remove the filters% gently s3uee,e out most of the j uice% and lay them out flat on a paper towel to dry completely. /hen /hen cut the paper into small strips with scissors% about G02 wide by 0-42 long works well. =ow you can use your indicator paper to test the p( of your test solutions% or other common household li3uids. 5ou can either dip a small portion of one strip in the test solution% or use a toothpick% H-/ip H-/ip or small straw to place a drop of the li3uid onto the paper strip. It should produce the same color change as you saw in the first part of this experiment if it doesn#t% you may not have stained your coffee filter sufficientlytry soaking the paper a little longer$.

"e#erences and lin$s to more in#ormation *thers versions of this activity:

http:GGchemistry.about.comGodGacidsbaseGaGred-cabbage-ph-indicator.htm http:GGwww.sciencebuddies.org http:GGwww. sciencebuddies.orgGscience-fair-p Gscience-fair-projectsGprojectideas rojectsGprojectideasG&hemp84.shtml G&hemp84.shtml http:GGwww.stanford.eduGJa http:GGwww. stanford.eduGJajspakowGdownlo jspakowGdownloadsGoutreachG adsGoutreachGph-student-K-48-8 ph-student-K-48-8K.pdf  K.pdf 

ore on acids and bases: http:GGwww.chem6kids.comGfiles http:GGwww. chem6kids.comGfilesGreactacidbas Greactacidbase.html e.html http:GGwww.funsci.comGfun http:GGwww. funsci.comGfun4enGacidsGacids 4enGacidsGacids.htm .htm